Chloe Kim

Photograph ByBrett Wilhelm/ESPN

Last January, American snowboarder Chloe Kim, then 13, made her X Games debut in Snowboard SuperPipe. She got a silver medal, not all that far behind veteran champion Kelly Clark, who took gold. Kim wasn't even old enough to compete at the Sochi Olympics, but she could have been a top contender there, as well. Now 14, she'll be Clark's biggest threat in the years to come.